1. Field of the Invention
The present invention relates to a vehicle-mounted radio wave radar for detecting a variable such as a distance or relative speed between a host vehicle (radar-loaded vehicle) and a target in front of the host vehicle.
2. Description of the Related Art
There is known a vehicle-mounted radio wave radar for detecting a variable such as a distance or relative speed between a host vehicle and a target, e.g., another vehicle or an obstacle, in front of the host vehicle by using radio waves of the millimeter-wave (EHF) band (60-77 GHz) in which radio wave beams are less attenuated even in foggy or other bad weather and are able to propagate over a long distance.
Examples of such a vehicle-mounted radio wave radar are disclosed in JP, A, 10-79616 and 10-261917.
In the former JP, A, 10-79616, a radome and a housing are employed to provide a structure for enclosing, e.g., an antenna, a high-frequency circuit section for processing a transmitted/received signal in the same high-frequency range as the transmitted/received signal, and a control circuit section for processing the transmitted/received signal in a relatively low-frequency range and performing other required processing. With this structure, the antenna is covered from front by the radome made of a material, such as a resin, which is transparent to electromagnetic waves of the millimeter-wave band with high efficiency, and the remaining part is covered by the housing. The latter JP, A, 10-261917 employs a structure that an antenna, a high-frequency circuit section and a control circuit section are stacked in a housing in this order and fixed to the housing by screws or the likes, and that a ground potential metallic layer is provided between the high-frequency circuit section and the control circuit section.
In the conventional vehicle-mounted radio wave radars described above, ground terminals of the components, i.e., the control circuit section and the high-frequency circuit section, are connected to a ground terminal of a battery remote from the position at which the radar is attached to a vehicle body. The ground terminal of the battery is connected to the vehicle body for grounding. Accordingly, impedance of a certain value depending on wires, body, and other vehicle parts exists between the ground terminals of the control circuit section and the high-frequency circuit section, the ground terminal of the battery, and the vicinity of the position at which the radar is attached to the vehicle body.
The presence of such impedance generates a noise loop through those vehicle parts and may deteriorate the performance of the vehicle-mounted radio wave radar because useless noises and static electricity are applied to the vehicle-mounted radio wave radar.
Further, when the components of the vehicle-mounted radio wave radar are stacked in a housing and fixed to the housing by screws or the likes as disclosed in the latter JP, A, 10-261917, the assembly work is difficult to implement because the housing is usually designed to have the least necessary size just enough to accommodate the components for a size reduction.
Accordingly, it is an object of the present invention to provide a vehicle-mounted radio wave radar which can restrain a deterioration of the performance caused by adverse effects of useless noises and static electricity. Another object of the present invention is to facilitate assembly work of the vehicle-mounted radio wave radar.
To achieve the above object, according to a first aspect of the present invention, a vehicle-mounted radio wave radar comprises a transmitting/receiving unit for transmitting and receiving a radio signal; a signal processing unit for processing the radio signal transmitted and received by the transmitting/receiving unit; an electrically conductive housing for accomodating the signal processing unit therein; an electrically conductive support plate supporting the transmitting/receiving unit and disposed so as to close an opening of the electrically conductive housing; and an insulating member for electrically isolating the electrically conductive housing and a vehicle body from each other. Ground lines of the transmitting/receiving unit and the signal processing unit are electrically connected to the electrically conductive housing and the electrically conductive support plate.
According to the first aspect, the ground lines of the transmitting/receiving unit and the signal processing unit, which are electronic parts constituting the vehicle-mounted radio wave radar, are electrically connected to the electrically conductive housing and the electrically conductive support plate. Also, the electrically conductive housing is electrically isolated from the vehicle body by the insulating member. Therefore, the transmitting/-receiving unit and the signal processing unit are electrically shielded by the ground potential of themselves, and hence adverse effects of useless noises and static electricity are reduced.
Also, according to a second aspect of the present invention, a vehicle-mounted radio wave radar comprises a transmitting/receiving unit for transmitting and receiving a radio signal; a signal processing unit for processing the radio signal transmitted and received by the transmitting/-receiving unit; an electrically conductive housing for accommodating the signal processing unit therein; an electrically conductive support plate supporting the transmitting/receiving unit and disposed so as to close an opening of the electrically conductive housing; and a capacitive device having one end connected to the electrically conductive housing and the other end connected to the vicinity of a position at which the vehicle-mounted radio wave radar is attached to a vehicle body, the capacitive device electrically connecting the electrically conductive housing and the vehicle body to each other through capacitive impedance. Ground lines of the transmitting/receiving unit and the signal processing unit are electrically connected to the electrically conductive housing and the electrically conductive support plate.
According to the second aspect, the ground lines of the transmitting/receiving unit and the signal processing unit, which are electronic parts constituting the vehicle-mounted radio wave radar, are electrically connected to the electrically conductive housing and the electrically conductive support plate. Also, the electrically conductive housing is electrically connected to the vehicle body through the capacitive device. Therefore, the transmitting/receiving unit and the signal processing unit are electrically shielded by the ground potential of themselves. In addition, a surge, which is produced by the transmitting/receiving unit and the signal processing unit due to a potential difference between the ground potential of themselves and the ground potential in the vicinity of the position at which the radar is attached to a vehicle body, is absorbed by the capacitive impedance of the capacitive device. As a result, adverse effects of useless noises and static electricity are further reduced in comparison with the radar according to the first aspect.
Further, according to a third aspect of the present invention, a vehicle-mounted radio wave radar comprises a transmitting/receiving unit for transmitting and receiving a radio signal; a signal processing unit for processing the radio signal transmitted and received by the transmitting/-receiving unit; an electrically conductive inner housing for accommodating the signal processing unit therein; an electrically conductive support plate supporting the transmitting/receiving unit and disposed so as to close an opening of the electrically conductive housing; an electrically conductive outer casing for accommodating the electrically conductive inner housing therein; and a capacitive device having one end connected to the electrically conductive inner housing and the other end connected to the electrically conductive outer casing, the capacitive impedance device electrically connecting the electrically conductive inner housing and the electrically conductive outer casing to each other through capacitive impedance. Ground lines of the transmitting/receiving unit and the signal processing unit are electrically connected to the electrically conductive inner housing and the electrically conductive support plate, and the electrically conductive outer casing is electrically connected to a vehicle body.
According to the third aspect, the ground lines of the transmitting/receiving unit and the signal processing unit, which are electronic parts constituting the vehicle-mounted radio wave radar, are electrically connected to the electrically conductive inner housing and the electrically conductive support plate. Also, the electrically conductive inner housing is electrically connected to the electrically conductive outer casing that is in turn electrically connected to the vehicle body through the capacitive device. As a result, as with the second aspect, adverse effects of useless noises and static electricity are further reduced in comparison with the radar according to the first aspect.
Moreover, according to a fourth aspect of the present invention, a vehicle-mounted radio wave radar comprises a transmitting/receiving unit for transmitting and receiving a radio signal;
a signal processing unit for processing the radio signal transmitted and received by the transmitting/-receiving unit; an electrically conductive housing for accommodating the signal processing unit therein; and an electrically conductive support plate supporting the transmitting/receiving unit and disposed so as to close an opening of the electrically conductive housing. The electrically conductive housing is electrically connected to a vehicle body, and impedance between a ground terminal of the signal processing unit and the electrically conductive housing is kept small to such an extent that a potential difference produced therebetween is negligible.
According to the fourth aspect, the electrically conductive housing is electrically connected to the vehicle body so as to keep the impedance between the ground terminal of the signal processing unit and the electrically conductive housing small to such an extent that the potential difference produced therebetween is negligible. As a result, the generation of useless noises and static electricity attributable to a noise loop can be restrained.
Additionally, in the vehicle-mounted radio wave radar according to any of the above aspects of the present invention, the radar may be assembled by placing the signal processing unit within the electrically conductive housing while a biasing unit is arranged on the side (same side as the opening of the electrically conductive housing) above the signal processing unit and/or the side (same side as the bottom of the electrically conductive housing) below the signal processing unit; and arranging the electrically conductive support plate supporting the transmitting/-receiving the in the opening of the electrically conductive housing, in which the signal processing unit is placed, in such a manner that the signal processing unit is fixedly positioned within the electrically conductive housing by a biasing force imposed from the biasing unit.
With those features, the signal processing unit can be fixedly positioned within the electrically conductive housing with no need of using screws or the likes, and the assembly work can be facilitated.